It's always intended as a compliment. And so I try to graciously accept it as one.
But I don't think I'm that unusual. Parents find themselves doing all sorts of things which they never thought they could or would do. When I was a teenager, I thought that my revulsion for dirty diapers pretty much made me parent-incompatible. (Personally, I think this is a birth control tactic which is being seriously overlooked.)
I find it curious that we have these two messages: we tell parents that 'it's different when it's your child' which is true. All the rules of disgust fly out the window when we care about someone. But we also act as if the reality of caring for children has limits. Whether your child kills someone, is developmentally disabled or simply a mooching burden, it's always different when it's your kid.
Maybe we should stop putting these parents on pedestals and start providing real supports so they don't have to feel alone and out on a limb for caring about their children.